Calibration of electric circuit breakers



Oct. 30, 1951 R. T. CASEY 2,573,307

CALIBRATION 0F ELECTRIC CIRCUIT BREAKERS Filed May 5, 1949 Inventor;

RobertTCasey,

is At or-ney.

Patented Oct. 30, 1951 CALIBRATION OF ELECTRIC CIRCUIT BBEAKE Robert T. Casey, Bristol, Conn., assignor, by

mesne assignments, to General Electric Company, a corporation of New York Application May 3, 1949, Serial No. 91,085

9 Claims. I

My invention relates particularly to devices which are automatically actuated to break a circuit upon a predetermined or rated overload, or 'upon a sudden surge and which can be actuated manually to open or close a circuit or to reset the mechanism after an automatic breaking of the circuit.

In small circuit breakers of this type, it has heretofore been the common practice to thread the calibrating screw into the body of the casing and allow its inner end to bear against the bimetal strip or bimetal support. Adjustment is then secured by turning the calibrating screw in or out to move the bimetal or its support to the desired position.

In such structure, the bimetal is retained in position against the tip of the calibrating screw by its own resiliency or by the resiliency of its support. With such a structure, a severe shock or vibration can cause the bimetal to move away from the tip of the screw and cause false tripping. Perhaps a more serious diificulty arises from the fact that since the resilience of the bimetal or its support is utlized to maintain the bimetal in its proper position, certain stresses are set up in these parts.

When a short circuit occurs these parts hecome exceedingly hot, with the result that they become, for a very short time, very soft, and the stresses set up in them are relieved, or altered, so that when the breaker has cooled and is reset, its calibration is quite often altered to such an extent as to render the breaker useless thereafter.

One object is to provide a means of adjustably positioning a trip releasing element with respect to the breaker casing.

Another object is to provide an adjusting means which will hold the adjusted element in position regardless of changes in stress or resilience of adjacent portions.

Another object is to provide such a means for In the form shown, the mechanism is supported in a housing formed of two parts and I have shown two ways of effecting calibration.

Fig. 1 is a view of one-half of the housing with the parts of mechanism 01' one form in the closed circuit position.

Fig. 2 is a fragmentary sectional view taken on the plane of the line 22 of Fig. 1.

Fig. 3 is a fragmentary sectional view taken on the plane of the line 3-3 of Fig. 1.

Fig. 4 is a fragmentary view similar to Fig. 1 but showing another form of calibrating device.

Fig. 5 is an exploded perspective view showing parts of the calibration device of Fig. 4.

The housing is formed of two molded insulating parts I, I held together by rivets or screws 8 and l. The circuit terminals l0 and II are suitably supported in the opposite ends of the housing.

In this form, the stationary switch contact 12 is formed on the inner end of the circuit termi nal Ill. The movable switch contact member I3 is hinged at H in the cradle or trip arm IS.

The bimetal strip or thermostatic member I6 is supported at one end by a bendable arm II which is connected to circuit terminal II. The calibrating screw [8 has its head positively positioned ina recess is in the housing and has a screw threaded stem fitted in the end of the arms I! and It so that the bimetal arm may be adjusted by rotating the screw I8 and thereby bending arm l1 and displacing the bimetal arm.

adjustably positioning a trip element with re- In order to insure that the calibration will not be altered thereafter, it is necessary to fix the screw in some manner. This may be done by filling in the recess near the head of the screw with some compound which will harden in a short time, such as Sauereisin" cement. For applications where the breaker is subject to a considerable amount of vibration, however, it is desirable that the calibrating screw be more permanently fixed, as for example by soldering. This is ordinarily done by putting a drop of solder on the screw threads binding the screw to the object it is threaded into. In the present design, however, a special anchoring means is provided which is available from the outside of the breaker after the breaker is completely assembled. For this purpose, I provide a hole extending transversely through both halves of the circuit breaker casing. After assembly and calibrating, a pin I9 is inserted so as to lie close to the head of the screw ll. A drop of solder is then placed in the recess, binding the pin to the screw-head and positively preventing any rotation of the screw under subsequent shock or vibration.

A flexible conductor 2| connects the switch member I! with the thermostatic member l6 and passes by a magnetic field piece 22 where it is held by a cover plate 23 which is gripped by the edges of the magnet 22.

The armature 24 is hinged 'at 25 to the arm l and has a heel 28 which normally engages the lug 21 on the end of bimetal strip l6 and thus acts as a latch. The armature is biased by spring 28 to turn clockwise as viewed in Fig. 1.

The finger piece or actuating lever 30 is pivoted at Si in the housing and connected by spring 32 to the switch member l3 near its center. The

arm H which carries the pivot point for the switch member i3 is itself pivoted at 33 in the housing.

To open the switch manually, it is only necessary to throw the lever 30 toward the right whereupon the toggle action will throw the switch member it to the ofi position. The circuit may be manually closed by moving the lever 30 back to the left.

In case the load exceeds the rated capacity of the circuit breaker the bimetal strip 56 will warp and release the latch 27 from the heel of the armature and thus permit the spring 32 to turn the arm is about its pivot 33 and release the switch member i3 and break the circuit.

, In case of a sudden heavy surge of current, the armature is drawn down and the latch 2i released suddenly and the circuit opened by the actuation of spring 32. The lever to then occupies a midposition but may be reset to the ofi position and returned to the on position when desired.

In the form shown in Fig. 4, the-calibration screw lfla is threaded into the housing and has a roove I8b to receive the notched end ll of the arm l1 so that the bimetal may be positively moved back and forth by rotating the screw. The parts are assembled by first inserting the screw and then inserting the bimetal support assembly, engaging the slotted or notched end in the grooves of the screw by angling it into po sition. When properly adjusted, the screw will be sealed in the recess l9a.

By reason of the method of mounting the bimetal arm and the calibrating screw in the housing, there is no possibility of achange in the calibration due to wear-or corrosion of the bimetal or the screw.

By means of the present structure, I provide a means for positively holding the controlled point iromrelative movement in any direction and this will not be altered by the relieving of any stresses in the bimetal or its support.

Another advantage is that positive control in both directions is achieved so thata push or a pull may be exerted on the bimetal or its support.

The mechanism for circuit breakers disclosed'in this application is claimed in application Number 237,256, filed July 17, 1951. i

I claim:

1. In a circuit breaker, an insulating housing, a movable arm supported in the housing, a thermostatic member having oneend secured to said arm, calibrating screw mounted in the housing and coacting with said arm to bend said arm back and forth and having its head positioned in a recess in the housing and accessible from the outside and a pin in the recess disposed transversely to the head otthe screw and sol- 76 improvements in automatic tripping,

dered thereto ior sealin said screw in the housing ing screw rotatable in an integral wall of said housing member and connected to said supporting member, means for positively preventing longitudinal movement or the screw relative to one member and screw means of connection with, the other member so that by rotating said screw said supporting member can be moved toward or from said housing member and means for scal ing said screw in place after adjustment including a transverse pin soldered to said screw within said housing.

4. A circuit breaker comprising a thermostatic arm having a supporting member, an insulating housing member enclosing said parts, a calibrating screw rotatable-in an integral wall of said housing member and connected to said supporting member, one end of said screw being rotatable without any relative longitudinal move-' ment in one member, and the other end of said screw having a screw threaded connection with the other member, and means for sealing said screw in place after adjustment including a transverse pin soldered to said screw within said housing.

5. In an electric circuit breaker having an insulating housing and an adjustably mounted member within said housing, means for adjusting said member including a screw havingv a main threaded portion having threaded engagement with said adjustably mounted member and an enlarged head portion larger in diameter than said main threaded portion, said insulating housing comprising two cooperating sections, the meeting faces of said cooperating sections having recesses therein adapted to closely surround said enlarged head portion of said calibrating screw when in assembled position so as to pre-.' vent substantially all movement of said calibrating screw other than rotational movement, and an opening from the exterior of said housing communicating with said recesses so as to permit rotation of said calibrating screw .from the exterior of said housing even though said cooperating sections are in assembled relation.

6. In a circuit breaker having a stationary contact and a cooperating movable contact, a manually movable operating member for moving said movable contact to open and closed circuit positions, means including a current-responsive.

' member for releasably restraining said movable contact in closed circuit position, an insulating housing enclosing all of the aforesaid parts other than the manually engageable portion of said operating member, and control means for adjustably positioning at least a portion of said restraining means, said control means including a calibrating screw having a main threaded por-- tion having a threaded engagement with said portion of said restraining means, and a head portion larger in diameter than said main threaded portion, said insulating housing comprising two cooperating sections, the meeting faces of said cooperating sections having recesses therein adapted to closely surround said enlarged head portion of said calibrating screw when in assembled position so as to prevent substantially all movement of said calibrating screw other than rotational movement, and an opening from the exterior of said housing communicating with said recesses so as to permit rotation of said calibrating screw from the exterior of said housing even though said cooperating sections are in assembled relation.

7. In an electric circuit breaker having an insulating housing and a member therein adjustable to vary the calibration of said circuit breaker, means for controlling the positioning of said adjustable member with respect to said housing, said means including a calibrating screw having a threaded engagement with said adjustable member and a rotational but axially substantially immovable engagement with an integral wall of said housing, said calibrating screw being accessible for adjustment from the exterior of said circuit breaker, and means for preventing accidental rotation of said calibrating screw including a transverse pin soldered to said screw within said housing.

8. In a circuit breaker, a thermostatic device having a supporting member, an insulating housing for the thermostatic device having a wall member, a calibrating screw supported by said wall member and connected to said supporting member, said screw having a threaded adjustable connection with said supporting member and a positive socket connection with said wall member whereby the thermostatic member and its supporting member may be adjusted back and forth by rotating the screw and means for sealing the screw in the housing wall including a transverse pin soldered to said screw within said housing.

9. In a circuit breaker, an insulating housing formed of two parts, breaker mechanism enclosed between said parts including a bracket supported by one of said parts and having a movable arm, a thermostatic latch member having one and secured to said movable arm, a calibrating screw having a slotted head rotatably mounted between said parts and having a rotatable connection with said movable arm for adjusting said arm and the attached thermostatic latch member, said parts having a recess providing access to said head, a-pin extending transversely of said head in said recess and soldere across the head of said screw.

ROBERT T. CASEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Krieger Nov. 9, 1948 

